This invention relates to the assessment of path imbalance in mobile communications networks, for example GSM mobile telephone networks.
Mobile communications networks, such as GSM mobile telephone networks, are showing continued rapid growth in deployment and adoption by users. Accordingly it is increasingly important that the design and operation of such networks are implemented to provide effective and efficient use of scarce radio spectrum resources.
A key parameter in GSM mobile telephone networks is the difference in received signal strengths at a mobile station (MS), such as a telephone handset, and at a fixed base station (BS) communicating with that MS. Network operators plan their network according to several parameters, including a target path imbalance figure that is chosen based on various characteristics such as the type of base station equipment to be used and the maximum transmit power for a selected one of several possible classes of mobile station defined for GSM systems.
Assessing the actual path imbalance figure achieved across a network can assist a network operator in highlighting areas of the network that are not performing as expected, e.g. because of faults in base station transmitter or receiver circuits. This can be accomplished in a GSM network, for example, by using messages which are received in base station controllers (BSCs) from their associated base transceiver stations (BTSs), and which contain received signal level (Rx Level) measurements both for the MS (measured at the BS) and for the BS (measured by the MS).
However, these Rx Levels must be corrected for the effect of power control in the relevant transmitter circuits, because path imbalance is defined assuming that both the MS and the BS are transmitting at full power. As the different possible classes of MS have different maximum transmit powers, using conventional methods a path imbalance figure must be calculated for each specific class (combining path imbalance figures for different mobile classes would distort the result). This requires significant processing effort to implement, especially as multiple messages relating to a call involving an MS must be tracked to enable the relevant MS class to be determined (from one kind of message) and associated with the signal level measurements for that MS (from other messages of a different kind).
It is an object of this invention to facilitate the derivation of path imbalance figures.
According to one aspect of this invention there is provided a method of assessing path imbalance in a mobile communications network having mobile stations in at least two classes of different maximum signal transmission power level, comprising the steps of:
selecting one of said classes as a reference class;
setting a reference mobile station power level equal to the maximum signal transmission power level of said reference class;
receiving a message from a mobile station indicative of the strength of signals transmitted by a base station and received by the mobile station, and of a power control level currently in use by the mobile station;
determining the strength of signals transmitted by the mobile station and received by the base station, and the power control level currently in use by the base station; and
determining the path imbalance in accordance with the relationship
Imbalance=(MS RxLevel+n*(MS Power Control Levelxe2x88x92Reference MS Power Level))xe2x88x92(BS Rx Level+n*BS Power Control Level)
where MS Rx Level is the strength of signals transmitted by the mobile station and received by the base station; MS Power Control Level is the power control level currently in use by the mobile station; Reference MS Power Level is said reference mobile station power level; BS Rx Level is the strength of signals transmitted by a base station and received by the mobile station; BS Power Control Level is the power control level currently in use by the base station; and n is a predetermined constant.
The value of n may vary depending on the specific network technology used; for a GSM network it will have a value of 2.